A client/server helper wrapper for endpoints in Go.

go/src/infra/gae/epservice/example/service_cas.go

Index: go/src/infra/gae/epservice/example/service_cas.go
diff --git a/go/src/infra/gae/epservice/example/service_cas.go b/go/src/infra/gae/epservice/example/service_cas.go
new file mode 100644
index 0000000000000000000000000000000000000000..f01804ec488218dcbfcd47732a3885d8319f929f
--- /dev/null
+++ b/go/src/infra/gae/epservice/example/service_cas.go
@@ -0,0 +1,52 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package example
+
+import (
+	"golang.org/x/net/context"
+	"infra/gae/libs/wrapper"
+	"infra/gae/libs/wrapper/gae"
+
+	"github.com/GoogleCloudPlatform/go-endpoints/endpoints"
+)
+
+// CASReq is the input for the CAS RPC
+type CASReq struct {
+	Name string `endpoints:"required"`
+
+	OldVal int64 `json:",string"`
+	NewVal int64 `json:",string"`
+}
+
+// CAS does an atomic compare-and-swap on a counter.
+func (Example) CAS(c endpoints.Context, r *CASReq) (err error) {
+	success := false
+	ds := wrapper.GetDS(gae.Use(context.Background(), c))
+	err = ds.RunInTransaction(func(context.Context) error {
+		ctr := &Counter{ID: r.Name}
+		if err := ds.Get(ctr); err != nil {
+			return err
+		}
+		if ctr.Val == r.OldVal {
+			success = true
+			ctr.Val = r.NewVal
+			_, err := ds.Put(ctr)
+			return err
+		}
+		success = false
+		return nil
+	}, nil)
+	if err == nil && !success {
+		err = endpoints.ConflictError
+	}
+	return
+}
+
+func init() {
+	mi["CAS"] = &endpoints.MethodInfo{
+		Path: "counter/{Name}/cas",
+		Desc: "Compare and swap a counter value",
+	}
+}